An in vitro study of the susceptibility of mobile and cystic forms of Borrelia burgdorferi to hydroxychloroquine.

Brorson O, Brorson SH.

In this work the susceptibility of mobile and cystic forms of Borrelia burgdorferi to hydroxychloroquine (HCQ) was studied.

• The minimal bactericidal concentration (MBC) of HCQ against the mobile spirochetes was
• > 32 microg/ml at 37 degrees C, and
• > 128 microg/ml at 30 degrees C.
• Incubation with HCQ significantly reduced the conversion of mobile spirochetes to cystic forms.
• When incubated at 37 degrees C, the MBC was
•  > 8 microg/ml for young biologically active cysts (1-day old), but it was
• > 32 microg/ml for old cysts (1-week old).
(compare with effective concentrations and toxic concentration given in GG)
• Acridine orange staining, dark-field microscopy and transmission electron microscopy revealed that the contents of the cysts were partly degraded when the concentration of HCQ was > or = MBC.
• At high concentrations of HCQ (256 microg/ml) about 95% of the cysts were ruptured (250 microg/ml is the toxic concentration).
• When the concentration of HCQ was > or = MBC, core structures did not develop inside the cysts, and the amount of RNA in these cysts decreased significantly.
• Spirochetal structures inside the cysts dissolved in the presence of high concentrations of HCQ.
• When the concentration of HCQ was > or = MBC, the core structures inside the cysts were eliminated.

PMID: 12102233 [PubMed - in process]

• Chloroquine Phosphate (ARALEN)
• Hydroxychloroquine Sulfate (PLAQUENIL)

Pharmacokinetic Data

CHLOROQUINE^a

Abbreviations:

a Active metabolite, desethylchloroquine, accounts for 20 ± 3% of urinary excretion; t_1/2 = 15 ± 6 days.
b Blood CL/F, Vss/F, and t_1/2; blood-to-plasma concentration ratio = 9.
c Shorter half-lives reported previously when sampling stopped after 1 month.
d Plasmodium vivax.
e Plasmodium falciparum.
f Diplopia; dizziness.

Reference:
White, N.J. Clinical pharmacokinetics of antimalarial drugs. Clin. Pharmacokinet., 1985, 10:187-215.

(added by J. Gruber)

• F   = body weight,
• Vss = steady state volume of distribution
• t_1/2 = elimination half life
• CL/F units = ml of blood compartment / (min kg of body weight)
• Enter body weight (e.g. 70 kg) and you have CL =  "total body clearance" in units ml of blood compartment / min.

Half Life

• peak plasma levels are achieved in about 3 to 5 hours after dosing by this route.

• from a few days
• to weeks

• The terminal half-life ranges from 30 to 60 days, and
• traces of the drug can be found in the urine for years after a therapeutic regimen.

Volume of Distribution V

The

1. plasma volume of a typical 70-kg man is 3 liters,
2. blood volume is about 5.5 liters,
3. extracellular fluid volume outside the plasma is 12 liters, and
4. the volume of total body water is approximately 42 liters.

Example:
If 500 mg of digoxin were in the body of a 70-kg subject, a plasma concentration C of approximately 0.7 ng/ml would be observed. Dividing the amount of drug in the body (500 mg) by the plasma concentration (0.7 ng/ml) yields a volume of distribution for digoxin of about 700 liters, or a value ten times greater than the total body volume of a 70-kg man.
In fact, digoxin, which is relatively hydrophobic, distributes preferentially to muscle and adipose tissue and to its specific receptors, leaving a very small amount of drug in the plasma.

Enrichment in Tissue, Brain, Spinal Cord

In animals the concentration 200 ... 700 times the plasma concentration may be found in

• liver
• kidney
• spleen
• lung.

The concentration in

• brain
• spinal cord

Explanations of usage of terms Clearance, Volume of Distribution, Half-Life

Following GG, General Principles, Chapter "Clinical Pharmacokinetics" in Leslie Benet "Pharmacokinetics" .

CL = Clearance from blood compartment (ml per minute)

(the notion used is that every minute a volume CL (ml) is removed (and freed of drug) from the volume of distribution Vss)

Example.
In GG-Appendix II, the "plasma clearance" for cephalexin is reported as CL/F = 4.3 ml  min-1 kg-1,

with 91% of the drug excreted unchanged in the urine.

For a 70-kg man, the "total body clearance from plasma" CL = 300 ml/min,

with renal clearance accounting for 91% of this elimination.

In other words, the kidney is able to excrete cephalexin at a rate such that approximately 273 ml of plasma would be freed of drug per minute.

Because clearance usually is assumed to remain constant in a stable patient, the total rate of elimination of cephalexin will depend on the concentration of drug in the plasma (equation 1-2).

useful definitions:

• Clearance

CL = (rate of elimination by specified route) / (Concentration in specified compartment)
 
• Elimination half life

t_1/2 = ln2/k = ln2 Vss/CL

Thus
CL = k Vss and
k = CL/Vss (= fraction of Vss removed per minute)
 

• Diff. eq. describing elimination:

dm/dt = - k m

(in GG k m is called "rate of elimination")
(equation 1-2)
rate of elimination = C CL =

                                         = C k Vss =
                                         = k C Vss = k m

with the following nomenclature:
C  = concentration of drug in blood (g drug/ml blood)
CL =  clearance ((ml blood / l volume of distribution) / minute)
k = elimination constant,
m = mass of drug (g)
rate of elimination = dm/dt = change of mass of drug in Vss per unit time

Dosage

Dosage may be taken in as multiples of D = 5 mg base per kg body weight, but D should not exceed 300 mg base:

1. first dose: 2 D,
2. 6 hours after the first dose: D.
3. 18 hours after the second dose: D,
4. 24 hours after the third dose: D .

• 200 mg of hydroxychloroquine sulfate (Plaquenil) is equivalent to 155 mg base.
• 500 mg of chloroquine phosphate (Aralen) is equivalent to 300 mg base

(2) Estimate of dosage to achieve a 32 microg/ml  concentration of free Chloroquine in blood (enrichment 1, i.e. no enrichment), tissue (enrichment 200), brain (enrichment 10)

If

• 100 % of the drug was bioavailable and
• 100 % of it free (not bound to other molecules),

intake1 = 32 microg/ml Vss = 224 g of base

Because

• availability is roughly 100 % and
• roughly half is bound to plasma proteins,

necessary intake = 2 intake1 = 448 g.

The dosage estimate is 448 g/ (2 t_1/2).

Although the high volume of distribution tells us that chloroquine distributes into compartments other than 1. - 4, and the concentration in those compartments is probably higher than the concentrations in blood, the GG data do not tell us how low the concentration in blood can be to yield a concentration of 32 microg/ml in Bb cyst infected tissue.

Using the enrichment data from Sanofi  and assuming an elimination half life t_1/2 = 41 + 14 days = 55 days, we will arrive at the following approximate dosages (numbers in parentheses ( ) apply to a half life t_1/2 = 41 - 14 days = 27 days)

1. dosage = 4000 (8000) mg/day for 32 microgram/ml in blood,
2. dosage = 20 (40) mg/day for 32 microgram/ml in tissue,
3. dosage = 400 (800) mg/day for 32 microgram/ml in brain.

• Roque MR, Foster CS, Chloroquine/Hydroxychloroquine Toxicity, e-medicine, 2004.
• Lyme and Hydroxychloroquine OR Amantadine